Oscillograph circuit to modulate a signal



Oct. 11, 1949. M. MARON 2,484,107

OSCILLOGRAPH CIRCUIT 'IO MODULATE A SIGNAL Filed Sept. 21, 1946 771M(NVENTOR.

RTTORNEI' phase are applied to the terminals 13 and B.

Patented Oct. 11,1949 4 OSCILLOGRAPH CIRCUIT TO MODULATE A SIGNAL MeyerMaron, Passaic, N. J., assignor to Allen B. Du Mont Laboratories, Inc.,Passaic, N. .L, a

corporation of Delaware Application September 21, 1946, Serial No.698,486

This invention relates to a circuit for a polar coordinate oscillograph.It is particularly useful for modulating a signal by means of anothersignal without using tuned circuits or filters. It will operate over. awide range of frequencies with little if any frequency discrimination,phase shift, or signal addition of modulating signal and signal to bemodulated.

With this invention radial deflection of the circular sweep of acathode-ray beam may be obtained by modulating the circular sweep withanother signal.

The invention, may be understood from the description in connection withthe accompanying drawing in which:

Fig.1 is a diagram of connections and elements illustrating anembodiment of the invention, and

Figs. 2 and 3 are diagrams showing, respectively, signals producedwithout and with this invention.

In the drawing, reference characters I, 2, 3 and 4 indicate pentodesthat are alike. They are of the same size and have like characteristics,The pentodes l and 2 have their plates connected to a source of positivepotential, not shown, through load resistance 5. The pentodes 3 and 4have their plates connected to the same source of positive potentialthrough load resistance 6.

The control grids of tubes 2 and 3 are negatively biased in the knownway as shown by the negative sign n and are coupled by condensers and 8respectively to input terminals A and A.

Balanced input signals of equal magnitude and 180 out of phase, that areto be modulated, are applied to the terminals A and A from which theyare applied to the control grids of the tubes 2 and 3 respectively.These signals A and. A may be direct coupled or they may be resistancecoupled from a source of such signals in the known way and are appliedto the control grids of the tubes 2- and 3 by condensers 1 and 8-Signals of equal magnitude and 180 out of The signal applied at B is fedto the screen grids of the tubes 2 and 3 and the signal applied at B isfed to the screen grids of the tubes I and 4. In this way thetransconductance of tubes 2 and 3 is changed and the signals A and A aremodulated. The' signals at B which are applied to the screen grids ofthe tubes I and 4 prevent distortion of the signal outputs from tubes 2and 3,

3 Claims. (Cl. 332-42) When the tubes l and 4 are not used the signalsapplied to the terminals A, A, are amplified by the tubes 2 and 3. Theseamplified signals are applied to the plates I5 and I5 and causedistortion of the modulated signals from tubes 2 and 3 as indicated inFig. 2. When the tubes I and 4 are connected as shown, the signalsapplied at A, A are modulated Without appreciable distortion as shown inFig. 3.

What is claimed is:

1. A device for modulating electrical signals which comprises acathode-ray tube having a pair of deflecting plates, a pair of pentodesto the control grids of which said signals are applied in phaseopposition, said grids being negatively biased, another pair ofpentodes, means to apply one phase of a modulating signal to the screengrids of said first named pair of pentodes and the opposite phase ofsaid modulating signal to the screen grids of said second named pair ofpentodes, and means to connect the outputs of the respective pairs ofsaid pentodes to opposite plates of said pairs of deflecting plates.

2. Apparatus for modulating a first electrical signal by a second signalcomprising a first pair of thermionic tubes having screen grids andnegatively biased control grids, said first signal being applied to saidcontrol grids respectively in phase opposition, a second pair ofthermionic tubes having screen grids and control grids, the output ofsaid second pair of tubes being connected respectively to the output ofsaid first pair of tubes, said second signal being applied to said vscreen grids of said first pair. of tubes and in opposite phase to'saidscreen grids of said second pair of tubes.

3. Apparatus for modulating afirst electrical signal by a second signalcomprising a. pair'of by compensatin for the rise in voltage at theplates of tubes 2 and 3, due to modulation.

Reference character T indicates a cathode-ray tube which is providedwith a cathode I I, control grid I2, first anode l3, second anode I4, apair I5, I 5' of vertical deflection plates and a pair I6, I6 ofhorizontal deflection plates.

The output appearing at the terminals 9 and I0 may be resistance coupledor it may be direct coupled to the vertical deflection of thecathode-ray tube T. l

thermionic tubes having anodes, screen grids and negatively biasedcontrol grids, said first signal being applied respectively in phaseopposition to said control grids, a second pair of thermionic tubeshaving anodes, screen grids and control grids and means for applyingsaid second signal to'the screen grids of said first pair of tubes andin opposite phase to the screen grids of said second pair of tubes, theanodes 01 said first pair 01' tubes being connected respectivelydirectly to the anodes or said second pair of tubes.

MEYER MARON.

REFERENCES CITED The following references are 01' record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,011,499 Paddle Aug. 13. 19352,239,776 Brunn Apr. 29, 1941 2,278,641 Bond Apr. 7,1942

